This invention relates generally to a vehicular disk brake apparatus and more particularly to the brake caliper thereof, which has a reinforced bridge for reducing load.
In general, a vehicular or automotive brake operates on a hydraulic system, in which the depression of a brake pedal causes a plunger in the master cylinder to push hydraulic fluid to a braking unit at the wheels. A disk brake is one kind of braking unit. In a conventional opposed caliper disk brake, a fixed caliper straddles a rotor, which is attached to the wheel. In a floating caliper disk brake, the caliper urges piston or pistons on one side of the rotor to apply a pad, while at the same time pushing the caliper housing away from the rotor, drawing the outboard pad up to the rotor. In either case, when fluid from the master cylinder is introduced into the caliper, it urges one or more pistons in the caliper to apply brake pad(s) against the rotor, thereby effectuating a braking force on the rotor and causing the wheel to slow down or stop.
A typical caliper is formed in the shape of a clam for straddling the rotor. Current designs either utilize a one piece housing, or two pieces, slit over the top of the rotor and held together by bolts. In straddling the rotor, one member is disposed on the inboard side of the rotor and the other member is disposed on the outboard side of the rotor. The members have piston(s) disposed therein.
A basic problem in calipers of this type is that they are subject to high shearing and bending forces, with the load bearing on the bridge section. When such forces are transmitted through the caliper, they act to spread the caliper apart like a clam, a phenomenon often referred to as the “clam shell” effect. The result is decreased braking efficiency, as some of the force generated by the master cylinder is lost in the spreading of the caliper, and there is also the consequent effect of increasing pedal travel, tapered pad wear, spongy pedal and loss of modulation.
To minimize this deflection, caliper designs have typically utilized either a monoblock or a bolting design. For example, in a monoblock caliper, the caliper is formed from a solid body with a bridge section integrally joining the inboard and outboard members of the caliper housing. This type of caliper requires a rather massive bridge section to effectively reduce the clam shell effect that causes the caliper to open at the bottom. A massive bridge is undesirable, however, as it gets in the way of maximizing the rotor diameter.
In a caliper where the members are connected by bolts, as shown in FIG. 1, there is still a clam shell effect, resulting in the pad cocking with respect to the rotor face, which causes an increase in pad drag and wear, and a decrease in braking efficiency. The key stress area of a caliper is typically within the pad boundaries, within the pistons. Although the use of a bolting connection may limit the growth of the outer portion of the caliper, it does nothing to stop the deflection below. In other words, the bottom of the caliper is free to open, and when subjected to high pressures, will still clamp back down on the rotor causing the pad to attempt to wedge into the rotor, causing taper.
For the foregoing reasons, there is a need for a disk brake assembly having a brake caliper that is sufficiently stiff to reduce the clam shell effect.